Boston requires energy audits from building owners. The city, along with Chicago and Philadelphia, passed measures to track how much energy buildings are using as a first step toward boosting their efficiency.

Other places including LA, Atlanta, Denver, Chicago, Houston and Salt Lake City, participate in a voluntary federal program to cut energy waste from commercial and industrial buildings.

Under the new effort, cities will work with the Natural Resources Defense Council (NRDC) and the Institute for Market Transformation, a nonprofit that promotes green building, to continue their progress and further shrink their carbon footprints by targeting existing commercial and apartment buildings.

The groups projected the emission reductions would be equal to taking more than a million cars off the road, and they could save residents and businesses $1 billion annually. The project is funded by ex-New York City Mayor Michael Bloomberg's foundation and other philanthropic groups, which invested $9 million for three years.

New York City managed to cut its emissions by persuading some landlords to switch from oil to natural gas, Bloomberg said.

Los Angeles Mayor Eric Garcetti said cities can be the matchmaker between building owners and banks that lend money for energy-efficient upgrades. He said greening buildings makes economic sense.

"We look forward to stealing your best ideas,'' he told other mayors.

The cities were chosen for their geographic diversity, ambitions and ability to follow through, said project director Laurie Kerr of the NRDC.

The cities will craft their plans in the next several months. Backers acknowledged that some policies may require legislation. It'll take several years to gauge whether cities met their emissions and savings goals.

Keith Crane, director of the environment, energy and economic development program at the Rand Corp. think tank, called the partnership a good first step. But he doesn't consider it earth-shaking.

"It'll have a modest effect on greenhouse gas emissions if everything goes right,'' he said.